77. Data Access

77.1 Configure a custom DataSource

To configure your own DataSource define a @Bean of that type in your configuration. Spring Boot will reuse your DataSource anywhere one is required, including database initialization. If you need to externalize some settings, you can easily bind your DataSource to the environment (see Section 24.7.1, “Third-party configuration”).

@Bean
@ConfigurationProperties(prefix="app.datasource")
public DataSource dataSource() {
    return new FancyDataSource();
}
app.datasource.url=jdbc:h2:mem:mydb
app.datasource.username=sa
app.datasource.pool-size=30

Assuming that your FancyDataSource has regular JavaBean properties for the url, the username and the pool size, these settings will be bound automatically before the DataSource is made available to other components. The regular database initialization will also happen (so the relevant sub-set of spring.datasource.* can still be used with your custom configuration).

You can apply the same principle if you are configuring a custom JNDI DataSource:

@Bean(destroyMethod="")
@ConfigurationProperties(prefix="app.datasource")
public DataSource dataSource() throws Exception {
    JndiDataSourceLookup dataSourceLookup = new JndiDataSourceLookup();
    return dataSourceLookup.getDataSource("java:comp/env/jdbc/YourDS");
}

Spring Boot also provides a utility builder class DataSourceBuilder that can be used to create one of the standard data sources (if it is on the classpath). The builder can detect the one to use based on what’s available on the classpath. It also auto detects the driver based on the JDBC url.

@Bean
@ConfigurationProperties("app.datasource")
public DataSource dataSource() {
    return DataSourceBuilder.create().build();
}

To run an app with that DataSource, all that is needed really is the connection information; pool-specific settings can also be provided, check the implementation that is going to be used at runtime for more details.

app.datasource.url=jdbc:mysql://localhost/test
app.datasource.username=dbuser
app.datasource.password=dbpass
app.datasource.pool-size=30

There is a catch however. Because the actual type of the connection pool is not exposed, no keys are generated in the metadata for your custom DataSource and no completion is available in your IDE (The DataSource interface doesn’t expose any property). Also, if you happen to only have Hikari on the classpath, this basic setup will not work because Hikari has no url parameter (but a jdbcUrl parameter). You will have to rewrite your configuration as follows:

app.datasource.jdbc-url=jdbc:mysql://localhost/test
app.datasource.username=dbuser
app.datasource.password=dbpass
app.datasource.maximum-pool-size=30

You can fix that by forcing the connection pool to use and return a dedicated implementation rather than DataSource. You won’t be able to change the implementation at runtime but the list of options will be explicit.

@Bean
@ConfigurationProperties("app.datasource")
public HikariDataSource dataSource() {
    return (HikariDataSource) DataSourceBuilder.create()
            .type(HikariDataSource.class).build();
}

You can even go further by leveraging what DataSourceProperties does for you, that is providing a default embedded database if no url is provided with a sensible username and password for it. You can easily initialize a DataSourceBuilder from the state of any DataSourceProperties so you could just as well inject the one Spring Boot creates automatically. However, that would split your configuration in two namespaces: url, username, password, type and driver on spring.datasource and the rest on your custom namespace (app.datasource). To avoid that, you can redefine a custom DataSourceProperties on your custom namespace:

@Bean
@Primary
@ConfigurationProperties("app.datasource")
public DataSourceProperties dataSourceProperties() {
    return new DataSourceProperties();
}

@Bean
@ConfigurationProperties("app.datasource")
public HikariDataSource dataSource(DataSourceProperties properties) {
    return (HikariDataSource) properties.initializeDataSourceBuilder()
            .type(HikariDataSource.class).build();
}

This setup puts you in pair with what Spring Boot does for you by default, except that a dedicated connection pool is chosen (in code) and its settings are exposed in the same namespace. Because DataSourceProperties is taking care of the url/jdbcUrl translation for you, you can configure it like this:

app.datasource.url=jdbc:mysql://localhost/test
app.datasource.username=dbuser
app.datasource.password=dbpass
app.datasource.maximum-pool-size=30
[Note]Note

Because your custom configuration chooses to go with Hikari, app.datasource.type will have no effect. In practice the builder will be initialized with whatever value you might set there and then overridden by the call to .type()`.

See Section 29.1, “Configure a DataSource” in the ‘Spring Boot features’ section and the DataSourceAutoConfiguration class for more details.

77.2 Configure Two DataSources

If you need to configure multiple data sources, you can apply the same tricks that are described in the previous section. You must, however, mark one of the DataSource @Primary as various auto-configurations down the road expect to be able to get one by type.

If you create your own DataSource, the auto-configuration will back off. In the example below, we provide the exact same features set than what the auto-configuration provides on the primary data source:

@Bean
@Primary
@ConfigurationProperties("app.datasource.foo")
public DataSourceProperties fooDataSourceProperties() {
    return new DataSourceProperties();
}

@Bean
@Primary
@ConfigurationProperties("app.datasource.foo")
public DataSource fooDataSource() {
    return fooDataSourceProperties().initializeDataSourceBuilder().build();
}

@Bean
@ConfigurationProperties("app.datasource.bar")
public BasicDataSource barDataSource() {
    return (BasicDataSource) DataSourceBuilder.create()
            .type(BasicDataSource.class).build();
}
[Tip]Tip

fooDataSourceProperties has to be flagged @Primary so that the database initializer feature uses your copy (should you use that).

Both data sources are also bound for advanced customizations. For instance you could configure them as follows:

app.datasource.foo.type=com.zaxxer.hikari.HikariDataSource
app.datasource.foo.maximum-pool-size=30

app.datasource.bar.url=jdbc:mysql://localhost/test
app.datasource.bar.username=dbuser
app.datasource.bar.password=dbpass
app.datasource.bar.max-total=30

Of course, you can apply the same concept to the secondary DataSource as well:

@Bean
@Primary
@ConfigurationProperties("app.datasource.foo")
public DataSourceProperties fooDataSourceProperties() {
    return new DataSourceProperties();
}

@Bean
@Primary
@ConfigurationProperties("app.datasource.foo")
public DataSource fooDataSource() {
    return fooDataSourceProperties().initializeDataSourceBuilder().build();
}

@Bean
@ConfigurationProperties("app.datasource.bar")
public DataSourceProperties barDataSourceProperties() {
    return new DataSourceProperties();
}

@Bean
@ConfigurationProperties("app.datasource.bar")
public DataSource barDataSource() {
    return barDataSourceProperties().initializeDataSourceBuilder().build();
}

This final example configures two data sources on custom namespaces with the same logic than what Spring Boot would do in auto-configuration.

77.3 Use Spring Data repositories

Spring Data can create implementations for you of @Repository interfaces of various flavors. Spring Boot will handle all of that for you as long as those @Repositories are included in the same package (or a sub-package) of your @EnableAutoConfiguration class.

For many applications all you will need is to put the right Spring Data dependencies on your classpath (there is a spring-boot-starter-data-jpa for JPA and a spring-boot-starter-data-mongodb for Mongodb), create some repository interfaces to handle your @Entity objects. Examples are in the JPA sample or the Mongodb sample.

Spring Boot tries to guess the location of your @Repository definitions, based on the @EnableAutoConfiguration it finds. To get more control, use the @EnableJpaRepositories annotation (from Spring Data JPA).

77.4 Separate @Entity definitions from Spring configuration

Spring Boot tries to guess the location of your @Entity definitions, based on the @EnableAutoConfiguration it finds. To get more control, you can use the @EntityScan annotation, e.g.

@Configuration
@EnableAutoConfiguration
@EntityScan(basePackageClasses=City.class)
public class Application {

    //...

}

77.5 Configure JPA properties

Spring Data JPA already provides some vendor-independent configuration options (e.g. for SQL logging) and Spring Boot exposes those, and a few more for hibernate as external configuration properties. Some of them are automatically detected according to the context so you shouldn’t have to set them.

The spring.jpa.hibernate.ddl-auto is a special case in that it has different defaults depending on whether you are using an embedded database (create-drop) or not (none). The dialect to use is also automatically detected based on the current DataSource but you can set spring.jpa.database yourself if you want to be explicit and bypass that check on startup.

[Note]Note

Specifying a database leads to the configuration of a well-defined Hibernate dialect. Several databases have more than one Dialect and this may not suit your need. In that case, you can either set spring.jpa.database to default to let Hibernate figure things out or set the dialect using the spring.jpa.database-platform property.

The most common options to set are:

spring.jpa.hibernate.naming.physical-strategy=com.example.MyPhysicalNamingStrategy
spring.jpa.show-sql=true

In addition all properties in spring.jpa.properties.* are passed through as normal JPA properties (with the prefix stripped) when the local EntityManagerFactory is created.

Spring Boot provides a consistent naming strategy regardless of the Hibernate generation that you are using. If you are using Hibernate 4, you can customize it using spring.jpa.hibernate.naming.strategy; Hibernate 5 defines a Physical and Implicit naming strategies: Spring Boot configures SpringPhysicalNamingStrategy by default. This implementation provides the same table structure as Hibernate 4. If you’d rather use Hibernate 5’s default instead, set the following property:

spring.jpa.hibernate.naming.physical-strategy=org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl

See HibernateJpaAutoConfiguration and JpaBaseConfiguration for more details.

77.6 Use a custom EntityManagerFactory

To take full control of the configuration of the EntityManagerFactory, you need to add a @Bean named ‘entityManagerFactory’. Spring Boot auto-configuration switches off its entity manager based on the presence of a bean of that type.

77.7 Use Two EntityManagers

Even if the default EntityManagerFactory works fine, you will need to define a new one because otherwise the presence of the second bean of that type will switch off the default. To make it easy to do that you can use the convenient EntityManagerBuilder provided by Spring Boot, or if you prefer you can just use the LocalContainerEntityManagerFactoryBean directly from Spring ORM.

Example:

// add two data sources configured as above

@Bean
public LocalContainerEntityManagerFactoryBean customerEntityManagerFactory(
        EntityManagerFactoryBuilder builder) {
    return builder
            .dataSource(customerDataSource())
            .packages(Customer.class)
            .persistenceUnit("customers")
            .build();
}

@Bean
public LocalContainerEntityManagerFactoryBean orderEntityManagerFactory(
        EntityManagerFactoryBuilder builder) {
    return builder
            .dataSource(orderDataSource())
            .packages(Order.class)
            .persistenceUnit("orders")
            .build();
}

The configuration above almost works on its own. To complete the picture you need to configure TransactionManagers for the two EntityManagers as well. One of them could be picked up by the default JpaTransactionManager in Spring Boot if you mark it as @Primary. The other would have to be explicitly injected into a new instance. Or you might be able to use a JTA transaction manager spanning both.

If you are using Spring Data, you need to configure @EnableJpaRepositories accordingly:

@Configuration
@EnableJpaRepositories(basePackageClasses = Customer.class,
        entityManagerFactoryRef = "customerEntityManagerFactory")
public class CustomerConfiguration {
    ...
}

@Configuration
@EnableJpaRepositories(basePackageClasses = Order.class,
        entityManagerFactoryRef = "orderEntityManagerFactory")
public class OrderConfiguration {
    ...
}

77.8 Use a traditional persistence.xml

Spring doesn’t require the use of XML to configure the JPA provider, and Spring Boot assumes you want to take advantage of that feature. If you prefer to use persistence.xml then you need to define your own @Bean of type LocalEntityManagerFactoryBean (with id ‘entityManagerFactory’, and set the persistence unit name there.

See JpaBaseConfiguration for the default settings.

77.9 Use Spring Data JPA and Mongo repositories

Spring Data JPA and Spring Data Mongo can both create Repository implementations for you automatically. If they are both present on the classpath, you might have to do some extra configuration to tell Spring Boot which one (or both) you want to create repositories for you. The most explicit way to do that is to use the standard Spring Data @Enable*Repositories and tell it the location of your Repository interfaces (where ‘*’ is ‘Jpa’ or ‘Mongo’ or both).

There are also flags spring.data.*.repositories.enabled that you can use to switch the auto-configured repositories on and off in external configuration. This is useful for instance in case you want to switch off the Mongo repositories and still use the auto-configured MongoTemplate.

The same obstacle and the same features exist for other auto-configured Spring Data repository types (Elasticsearch, Solr). Just change the names of the annotations and flags respectively.

77.10 Expose Spring Data repositories as REST endpoint

Spring Data REST can expose the Repository implementations as REST endpoints for you as long as Spring MVC has been enabled for the application.

Spring Boot exposes as set of useful properties from the spring.data.rest namespace that customize the RepositoryRestConfiguration. If you need to provide additional customization, you should use a RepositoryRestConfigurer bean.

[Note]Note

If you don’t specify any order on your custom RepositoryRestConfigurer it will run after the one Spring Boot uses internally. If you need to specify an order, make sure it is higher than 0.

77.11 Configure a component that is used by JPA

If you want to configure a component that will be used by JPA then you need to ensure that the component is initialized before JPA. Where the component is auto-configured Spring Boot will take care of this for you. For example, when Flyway is auto-configured, Hibernate is configured to depend upon Flyway so that the latter has a chance to initialize the database before Hibernate tries to use it.

If you are configuring a component yourself, you can use an EntityManagerFactoryDependsOnPostProcessor subclass as a convenient way of setting up the necessary dependencies. For example, if you are using Hibernate Search with Elasticsearch as its index manager then any EntityManagerFactory beans must be configured to depend on the elasticsearchClient bean:

/**
 * [email protected] EntityManagerFactoryDependsOnPostProcessor} that ensures that
 * [email protected] EntityManagerFactory} beans depend on the [email protected] elasticsearchClient} bean.
 */
@Configuration
static class ElasticsearchJpaDependencyConfiguration
        extends EntityManagerFactoryDependsOnPostProcessor {

    ElasticsearchJpaDependencyConfiguration() {
        super("elasticsearchClient");
    }

}